The Lifecycle of Geology in a Civil Engineering Project - Part 2

The Lifecycle of Geology in a Civil Engineering Project (Part 2)

Do Civil Engineers need to know any geology? Find out in our latest blog series which walks you through the lifecycle of a project and just why geology is key:

Geology for Initial Planning and Scoping

Geology for Construction Materials

Geology for Foundation Design

Geohazard Identification

Impacts of Geology on Construction

Geology for Construction Materials (Part 2)

Geology is the single most important factor in making and finding construction materials for civil engineering projects.

ALL natural construction materials are a function of the geological process that created it.

So, what kind of construction materials do we use in a civil project? A lot! Some are described below:

  • General fill material to build up ground levels.
  • Pavement materials for roads and hardstands.
  • Sand fill or aggregate/gravel material for drainage.
  • Clay fill material for impermeable layers like dam embankments and pond clay liners.
  • Large rocks for erosion protection on coastal walls and structures or where there are floodways (river crossings).
  • Aggregates to make concrete.
  • Clay to make bricks.

A typical road embankment detailing some of the different construction materials (The Local Government & Municipal Knowledge Base)

Knowing where these materials are likely to be present (and where they are not) has a huge impact on the development and design of a civil project.

The geological input is probably the most important factor in helping to identify these materials. For example, finding natural materials that are suitable for road pavement construction is pretty difficult in regional areas.

But knowing that you are looking for a well graded clayey sandy gravel material you might look for a high energy alluvial deposit. Like this:

Photograph of cut bank of alluvial channel (CMW Geosciences)

And, when it is placed on a road – it looks like this! 

Photograph of alluvial deposits placed and compacted to form a road pavement (CMW Geosciences)

Or you could look at areas of mixed colluvial/alluvial deposits coming down off large ridges:

Annotated map showing different sources of materials (original map from Google Earth, 2021)

These colluvial deposits look like this:

Example of colluvial deposits along rock ridge (CMW Geosciences)

If you are looking for clay fill material, you could look for low energy deposition areas, like supra/intertidal areas (mudflats):

Annotated map of areas of supra/intertidal deposits (original map from Google Earth, 2021)

If you are looking for some areas of hard rock that may be suitable for rock armour or rip rap, then looking for outcropping dolerite dykes could be the answer.

Area of potential hard rock from a dolerite dyke (original maps from Google Earth, 2021)

Without a good understanding of geology, finding useful construction materials is very difficult.

Combining the mapped geology, findings from geological mapping and associated intrusive investigations, suitable construction material borrow sources can be identified and mapped for use during construction.

The image below shows a combination of the geological inputs that are used to create a map:

Annotated map showing geological deposits, interpreted materials and potential area for construction materials (CMW Geosciences).

Once the materials have been found a geologist is also required to continue on during construction.

This could be to check out the suitability of the material as it is excavated. Because of their geological origins, they can be highly variable. Or it could be to look at the excavation of a rock quarry face:

The stability of the cut as well as the variability and suitability of the rock needs to be looked at.

The geologist’s job throughout this entire process is to make sure that the quarry and/or borrow pit is safe and to make sure that the material coming out is suitable for its intended purpose (rock armour/rip rap, pavements etc.)